1. Technical Field
The present application relates to a method for detecting an analyte and a detection system that are based on surface-enhanced Raman spectroscopy.
2. Description of the Related Art
In Raman spectroscopy, a substance is irradiated with monochromatic light (excitation light) of a certain frequency so that scattered light occurs therefrom, and any scattered light that has a different frequency (hereinafter referred to as Raman-scattered light) from the frequency of the incident light is spectropically detected. A difference (Raman shift) between the frequency of the Raman-scattered light and the frequency of the incident light is equal to the frequency which corresponds to the difference between energy levels of vibration or rotation of molecules and atoms in the molecule or crystal that composes a substance, and takes a value which is specific to the structure of the substance. Therefore, Raman spectroscopy is utilized to discover the structure and state of a molecule.
Among other Raman spectroscopy techniques, surface-enhanced Raman spectroscopy has been proposed, which utilizes surface-enhanced Raman scattering (SERS).
Surface-enhanced Raman scattering is a phenomenon in which Raman-scattered light from molecules that have adhered to the surface of a specially-designed sensor chip having a precious metal structure of nanometer size increases in intensity. Surface-enhanced Raman scattering provides an enhancement of usually about 104 to 109. This enables highly sensitive detection of molecules which are immobilized on a metal surface, or even molecules near the metal surface.
In the field of medical diagnosis, a wide range of applications of surface-enhanced Raman spectroscopy is being considered. Surface-enhanced Raman spectroscopy is especially applied to the detection of biological components such as glucose that is contained in a biological body. Furthermore, based on an intensity of surface-enhanced Raman-scattered light, the concentration of a biological component can be calculated.
International Publication No. 2006/090308 discloses a method of measuring the glucose concentration in a biological body. According to International Publication No. 2006/090308, a sensor chip is embedded near capillary blood vessels, and the intensity of surface-enhanced Raman-scattered light that may occur is measured, whereby the scattering effect of erythrocytes existing in the blood and the interference effects of signals from other components can be reduced. This enables detection of surface-enhanced Raman-scattered light with a good SN ratio.